This is a multicenter, double blind, randomized, placebo-controlled study of the onset and offset of hemodynamic effects and plasma drug concentrations following sustained infusions of opc-18790 in patients with nyha class III-IV heart failure. Opc-18790 is a phosphodiesterase inhibitor with direct inotropic effects. Unlike other inotropes, opc-18790 also possesses mild vasodilatory activity resulting in after load reduction. Inotrophy and vasodilatation, combined with opc's effect on sinus node automaticity, make his compound a promising new therapy for the treatment of advanced heart failure.